#4 and #7 firing order swap

[jackson]

I read about this here a while ago but I couldn't find it again.  I am ordering a new cam for our SB Chevy and the guy at Crane was trying to talk me into the firing order swap cam.  When I asked the benefits, he didn't really give me a very good explanation.  Does anyone have any feed back on this swap?

[GH]

Jack, when I ordered the cam when changing from the roots blower to the turbos, comp cams sold me the 7-4 swap, they told me it was to improve the harmonics in the crankshaft.

[El Wayno]

You can find articles in Hot Rod about em. Especially if you read their Engines quarterly published periodicles. Most seem to have found marginal gains, but a lot of top drag teams use em. Plus I believe the old ford small and chevy had the same firing order. On the ford the last two pistons on the driver side fire on after the other. Later on the 5.0 and 351 they made the swap. The 4-7 puts the chevy the same way. I believe it did have to do with crank harmonics and loading. If 8 fires right after 7 and the spark jumps wires or whatever it is a bigger problem than the other way round.

[Jonny Hotnuts]

I had heard about 4-7 swap a few years ago and thought it was BS or the improvement would not justify.

I have seen a motor dynoed with the same grind cam gain 15 hp from the 4-7 alone and I hear more is capable (and I hear the motor runs smoother as well).

Sense I have seen the results the 4-7 swap would be the first thing I would do if I were running a SB chev!

[wheels777]

This swap is more benficial on a BBC.  The #2 cylinder and the #7 cylinders are on the long runners and on opposite ends.  This is a particular issue with leaning out #2 because it pulls air/fuel after #5 and #7.  So the strong sequential pull to the back end is followed by #2, and #2 will run lean. 

The improvement by making the firing order change on a SBC is not as great because the intake valves on the end cylinders are on the inboard.  But there is some gain since the air flow change goes from the back of the engine to the middle, instead of to the front as in the "stock" firing arrangement.

[Stan Back]

So with port injectors, there'd be no advantage (?).

[SPARKY]

AT the very least---the crank harmonics are  better!!!!!!!!